1. Field of the Invention
This invention relates to a vehicle heating system equipped with a heater which can operate independently of a car engine.
2. Description of the Prior Art
Vehicle heating systems are disclosed in Japanese Patent Laid-Open No. 252018/1985 and Japanese Utility Model Laid-Open No. 59876/1986.
First of all, the vehicle heating system described in Japanese Patent Laid-Open No. 252018/1985 will be explained with reference to FIG. 6 of the accompanying drawings. In this vehicle heating system, a burner 104 for burning a fuel is disposed in an intake pipe 103 of an engine 101 and a heat exchanger 105 is disposed downstream of the burner 104 in order to provide heat exchange between the combustion gas generated by burning the fuel by the burner 104 and the air for heating, and the heating air thus heated is used for heating the car.
Next, the warming-up means of the engine described in Japanese Utility Model Laid-Open No. 59876/1986 will be explained with reference to FIG. 7. In the warming-up means, an intake detour circuit 4 is disposed in parallel with an intake pipe 3 of an engine 1 at an intermediate part of the intake pipe 3, a burner 5 and a heat exchanger 8 communicating with a car heater unit 9 are disposed sequentially in this intake detour circuit 4 and a pressure control valve 12 is disposed in the intake pipe 3 bypassing the intake detour circuit 4. The burner 5 is connected via a fuel pipe 6 to a fuel injection pump 32' fitted to the engine 1 and fuel from a fuel tank 11 is burnt by the burner 5 disposed in the intake detour circuit 4. The air outlet side of the heat exchanger 8 is connected to the heater unit 9 of the car so that the hot air warmed up through heat exchange with the combustion gas of the burner having carbureter means 7 flows into the heater unit 9.
A check valve 15 such as a lead valve is disposed upstream of a confluence point of the intake detour circuit 4 with the intake pipe 3 to prevent suction air from the intake pipe 3 side from entering the intake detour circuit 4 at its downstream side. A pressure control valve 12 is disposed at the portion of the intake pipe 3 where it bypasses the intake detour circuit 4. This pressure control valve 12 is disposed in order to keep always constant a differential pressure of the intake pipe 3 between upstream and downstream of the safety valve 12. This valve 12 includes an arm 12b which is fitted to a rotary shaft 12a and connected to a rod 13c formed projectingly from a diaphragm 13a of a diaphragm type actuator 13. A spring chamber 13b of the actuator 13 is connected to a negative pressure sensor 14 disposed in the intake pipe 3 downstream of the pressure control valve 12 by a communication pipe 13d, so as to introduce the pressure downstream of the pressure control valve 12 into the spring chamber 13b.
In the vehicle heating system shown in FIG. 6 and in the engine warming-up means shown in FIG. 7, the combustion gas is introduced into the intake pipe of the engine after passing through the heat exchanger of the heater, and the air for combustion which is sent in the burner of the heater is taken into from the air cleaner for the engine. As to the heat exchanger of the heater, heat exchange is made between the combustion gas and the heating air, that is, on the gas-to-gas basis. Accordingly, if the combustion gas mixes accidentally into the heating air during heat exchange between them, the combustion gas might enter the car. If unburnt gases such as CO, HC, and the like, are contained in this combustion gas, a critical problem that might prove fatal to the occupant may arise.
Furthermore, the size of a piping arrangement must be increased or a blower having a higher capacity must be disposed to minimize resistance in the case of air, depending upon types or models of cars, but such means are difficult to employ because of a limited capacity of a power source. In the case of the combustion gas, or in the case of the gas-to-air heat exchange, an air conditioner unit of a carburetor must be changed or modified structurally and this results in a more complicated construction and a more troublesome fitting work. Moreover, the heating system itself becomes more expensive, and still another problem will develop in that the heating air will be overheated when the car stops abruptly.